In paper processing and for the printing processes it is necessary to splice papers in order to ensure a continuous operation. The splicing operation, and hence the PSA splicing tapes, are subject to very stringent requirements, since even today operating speeds of more than 1 500 m/min are entirely common. PSA splicing tapes must have a good tack, but should also have a high dimensional stability, for exposure to shearing. As well as the adhesive-related requirements, the PSAs ought likewise to withstand the operation of recycling the paper; that is, after reprocessing, there should be no tackiness from the splicing tape remaining on the paper.
Moreover, in recent years, the reprocessing conditions for the paper recycling operation have changed. Formerly, reprocessing was carried out under acid conditions. At the present time the trend is towards reprocessing in a basic medium
With the aim of attaining the requirements referred to above, the patent literature has already described a large number of different PSA tapes. The first repulpable splicing tape was described in U.S. Pat. No. 2,838,421. There, polyacrylic acid was mixed with polypropylene glycol to produce a water-soluble PSA. U.S. Pat. No. 3,441,430 describes a repulpable PSA tape based on acrylic acid/ethyl acrylate copolymers and water-soluble plasticizers having at least one ether function.
U.S. Pat. No. 3,661,874 discloses epoxidized rubbers which have been reacted with secondary monoamines and compounded with water-soluble plasticizers. DE 2 360 441 describes copolymers of acrylates and vinylcarboxylic acids which have in part been neutralized with liquid polyoxyethylenes and/or with a reaction product of acidic resins and alkanolamines. The cohesion of these PSAs can be enhanced by using ethoxylated diamines as plasticizers (DE 3 105 894).
The splice strength at relatively high temperatures can be enhanced by using acrylamide (DE 3 901 690 and EP 0,081,846). Terpolymers of N-vinyllactams or N-vinylamides, acrylic acid and alkyl vinyl ethers, disclosed in DE-C 34 23 446, likewise produce an enhancement of splice strength at high temperatures. Acrylic acid can also be substituted by acryloyloxypropanoic acid (EP 0,352,442).
PCT/US 92/06731 discloses terpolymers composed of polar monomers, such as acids or hydroxyalkyl esters, for example, and less polar monomers, such as acrylate-based alkyl esters, for example, and of polymerizable, water-soluble macromonomers. These terpolymers have likewise been blended with water-soluble plasticizers and exhibited high repulpability within a wide pH range.
The polymers cited above, however, possess the disadvantage either that they cause problems in the alkaline reprocessing operation, by forming agglomerates, or that on papers containing calcium carbonate they likewise form agglomerates, which significantly lower the tack of the polymer during adhesive bonding for a prolonged period.
There is therefore a need for a pressure-sensitive adhesive which does not have the aforementioned disadvantages of the prior art.